Alloys for magnetic recording-reproducing heads

ABSTRACT

A ferromagnetic alloy of magnetic recording-reproducing heads, essentially consisting of 70.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% of iron, and 3.1 to 14.0 Wt.% of niobium, and having Vickers hardness of above 150 and a high initial permeability and a maximum permeability of above 3,000 and 5,000, respectively, and a degree of order greater than 0.1 but less than 0.6.

United States Patent [1 1 Masumoto et al.

[451 July 3,1973

ALLOYS FOR MAGNETIC RECORDING-REPRODUCING HEADS Inventors: Hakaru Masumoto, Sendai; Yuetsu Murakami, Miyagi; Masakatsu Hinai, Natori, all of Japan The Foundation: The Research Institute of Electric and Magnetic Alloys, Sendai, Japan Filed: June 17, 1971 Appl. N0.: 153,974

Assignee:

Foreign Application Priority Data June 25, 1970 Japan 45/54759 [56] References Cited UNlTED STATES PATENTS 1,873,155 8/1932 Scharnow l48/3l.55 1,910,309 5/1933 .Smith et a1... 148/3l.55 3,390,443 7/1968 Gould et a1. l48/3l.55 3,133,159 5/1964 Johnson 340/l74.l F

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. R. Satterfield Att0rneyYoung & Thompson [57] ABSTRACT A ferromagnetic alloy of magnetic recordingreproducing heads, essentially consisting of 70.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% of iron, and 3.1 to 14.0 Wt.% of niobium, and having Vickershardness of above 150 and a high initial permeability and a maximum permeability of above 3,000 and 5,000, respectively, and a degree of order greater than 0.1 but less than 0.6.

6 Claims, 11 Drawing Figures 'PATENTED JUL 3 I915 PAIENTED JUL 3 I975 SHEH'T'BF 9 ALLOYS FOR MAGNETIC RECORDING-REPRODUCING HEADS BACKGROUND OF THE INVENTION This invention relates to a high-permeability alloy for magnetic recording-reproducing heads, which alloy consists of 70.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% of iron, 3.1 to 14.0 Wt.% of niobium, and an inevitable amount of impurities. With the alloy of the present invention, a high permeability, a high hardness, and a high electric resistivity can be obtained through simple heat treatment, and the alloy can easily be formed into magnetic recordingrreproducing heads.

Permalloy (nickel-iron alloy) is widely used at the present in magnetic recording-reproducing heads of audio tape recorder, because it has a high workability. The conventional Permalloy, however, has a shortcoming in that its Vickers hardness I-Iv is in the order of about 130 and comparatively low, so that its abrasion resistivity is rather poor. Accordingly, there has been a pressing need for improving the hardness and abrasion resistivity of alloy materials for magnetic recording-reproducing heads.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to meet the aforesaid need-by providing an alloy having excellent hardness and abrasion resistivity, along with a high permeability.

To achieve the object of the invention, the applicants have carried out a series of tests on alloys, which have a permeability higher than that of binary Permalloy and high hardness and electric resistivity, while maintaining a high workability. As a result, the applicants have found out that, with the addition of 3.1 to 14.0 Wt.% of niobium into nickel-iron alloys, magnetic and mechanical properties of the alloy can noticeably be improved.

According to present invention, there is provided an alloy consisting of 70.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% of iron, 3.1 to 14.0 Wt.% of niobium, and an inevitable amount of impurities, which alloy has a high initial permeability, e.g., 3,000 or higher, a high maximum permeability, e.g., 5,000 or higher, a Vickers hardness greater than 150, and a high electric resistivity. The alloy of the invention can easily be heat treated and formed into the shape of magnetic heads, recording or reproducing. The heat treatment, according to the present invention for providing the desired high permeability andhigh hardness, comprises steps of heating the alloy in vacuo or in a non-oxidizing atmosphere, for the purpose of thorough solution treatment and homogenization, at 800C or higher, preferably 1,100C or higher, for at least 1 minute but not longer a process comprising steps of heating the alloy of the aforesaid composition in vacuo or in anon-oxidizing atmosphere, for the purpose of thorough solution treatment and homogenization, at 800C or higher, preferably 1,100C or higher, for at least 1 minute but not longer than about hours depending on the alloy composition; cooling the alloy to a'temperature above its order-disorder lattice transformation point, e.g., at about 600C, so as to keep the alloy at the last mentioned temperature for a short while until uniform temperature is established throughout the alloy; cooling the alloy from the temperature above the orderdisorder lattice transformation point to room temperature at a rate faster than 1C/hour but slower than 100C/second, depending on the alloy composition; reheating the alloy at a temperature below the orderdisorder lattice transformation point for at least 1 minute but not longer than 100 hours depending on the alloy composition; and cooling it to room temperature.

The aforesaid solution treatment should preferably be effected at a temperature above 1,100C, especially about 1,250C, instead of at a temperature of 800to 1,100C, for an extended period of time, so as to effect the solid solution treatment as throroughly as possible. The thorough solid solution treatment results in an outstanding improvement of the magnetic properties of v the alloy.

The manner in which the alloy is cooled from the solution treatment temperature to a temperature above its order-disorder lattice transformation point, e.g., to about 600C, does not affect its magnetic properties so seriously, regardless of whether it is cooled quickly or slowly. The cooling speed when the alloy temperature crosses its order-disorder lattic transformation point has profound effects on the magnetic properties of the alloy, and hence, it is necessary to cool the alloy from the order-disorder lattice transformation point at a rate faster than lClhour' but slower than 100C/second. Such range of the cooling speed is selected in order to causethe degreeoforder of the alloy to fall in a range of 0.1 to 0.6, preferably 0.2 to 0.5. If the alloy is comparatively quickly cooled at about 100C/second, its degree of. order becomes comparatively small, e.g., at about 0.1. Quick cooling faster than 100C/second results in a degree of order small than 0.1 and does not provide thev desired permeability. r I

0n the other hand, excessively slow cooling, slower than lC/hour, tends to make the degree of order too large in excess of 0.6, so that the desired-high perme ability cannot be achievedy The inventors have found that the permeability of the alloy of the invention can be maximized when the degree of order of the alloyfalls in a range of 0.1 to 0.6. The aforesaidcooling from a temperature above the order-disorder lattice transformation point of the alloy at a rate faster than 1C/hour but slower than 100C/second will results in the desireddegree of order in the range of 0.1 to 0.6. The permeability of the alloy thus treated, especially when it is quickly cooled, may be further improved by tempering or reheating it to a temperature below its order-disorder lattice transformation point, e.g., in a range between 200 and 600C. In short, with the present invention, the permeability of the alloy of the aforesaid composition is maximized by making its degree of order be'0. 1 to 0.6 by applying thorough solution treatment at 800C or higher, preferably l,l 00 to l,250C, followed by cooling at a proper rate in the aforesaid range. When quick cooling fails to provide the high permeability, the additional tempering, preferably in the range of 200 to 600C, will improve its degree of order for raising its permeability.

Generally, a higher treating temperature tends to allow a shorter treating time, while a lower treating temperature tends to require a longer treating time. Similarly, a greater mass tends to require a longer treating time, while a smaller mass tends to allow a shorter treating time.

In cooling the alloy having the aforesaid composition, according to the present invention, from a temperature above its order-disorder lattice transformation point to a low temperature, e.g., to room temperature, the proper cooling speed for maximizing its permeability somewhat varies depending on its composition, but the cooling speed to be used in the method of the present invention usually so slow that cooling in a furnace is preferred. With conventional nickel-iron alloys containing no niobium, e.g., Permalloy, high permeability cannot be obtained unless it is quickly cooled, for instance by forced-air-cooling. The difference of the cooling speed between the conventional alloys and the alloy of the present invention is a very important factor in improving the properties of magnetic material.

For instance, after shaping magnetic recordingreproducing heads, such heads are usually heat treated for eliminating internal stress caused in the heads by the shaping process. To retain their proper shape and to avoid the oxidation of their surface, slow cooling in a vacuo or in a non-oxidizing atmosphere is preferable. The conventional alloys requiring quick cooling for producing a high permeability is not suitable for such slow cooling. On the other hand, the alloy according to the present invention is particularly suitable for such post-shaping heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference is made to the accompanying drawings, in which:

FIG. 1A is a graph illustrating the relation between the composition of nickel-iron-niobium alloys and their initial permeability;

FIG. 1B is a graph illustrating the relation between the composition of nickel-iron-niobium alloys and their maximum permeability;

FIG. 2A is a graph representing sections along the lines a-a' of FIGS. 1A and 1B (FezNb 1.321);

FIG. 2B is a graph representing sections along the lines b-b' of FIGS. 1A and 1B (Ni:Nb 9.611);

FIG. 2C is a graph representing sections along the lines -0 of FIGS. 1A and 1B (NizFe 7.3:1);

FIG. 3A is a graph showing the relation between the initial permeability of Specimen No. 55 of the alloy according to the present invention and their heating temperature and heating time;

FIG. 3B is a graph showing the relation between the maximum permeability of Specimen No. 55 of the alloy according to the present invention and their heating temperature and heating time;

FIGS. 4A and 4B are graphs showing the effects of different cooling speeds on the initial permeability and the maximum permeability of the alloys of the present invention, respectively;

FIG'. 5 is a magnetic hysteresis curve of Specimen No. 55 of the alloy according to the present invention; and

FIG. 6 is a graph representing the effects of different niobium contents in the alloy according to the present invention on their electric resistivity and Vickers hardness, assuming a constant nickel content of about Wt.%.

DESCRIPTION OF THE PREFERRED EMBODIMENT A method for making an alloy according to the present invention will now be described step by step.

In order to make the alloy of the present invention, a suitable amount of a starting material consisting of 7.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% of iron, and 3.1 to 14.0 Wt.% of niobium (instead of metallic niobium, ferro-niobium available in market may also be used) is melted by a melting furnace in air, preferably in vacuo or in a nomoxidizing atmosphere; a small amount (less than 1 Wt.%) of a de-oxidizer and a desulfurizer, e.g., manganese, silicon, aluminum, titanium, calcium alloy, and the like, is added in the melt for removing impurities as far as possible; and the mo]- ten metal thus prepared is thoroughly agitated to homogenize its composition.

For the purpose of testing, a number of different alloy specimens were prepared in the aforesaid manner. Each of the alloy specimens was poured into a mold for producing an ingot. The ingot was then shaped into sheets, each being 0.3 mm thick. The alloys can be shaped into any other suitable form by forging or rolling at room temperature or at an elevated temperature.

Rings with an outer diameter of 35 mm and an inner diameter of 27 mm were punched out of the sheets thus prepared. The rings were then heated at 800C or higher, preferably at l,l00C or higher, for at least 1 minute but not longer than hours, in vacuo or in hydrogen or other non-oxidizing atmosphere, and then cooled at a cooling speed suitable for the composition of each alloy specimen in the range of lC/hour to 100C/second, preferably 10C/hour to 10C/second. For certain alloy compositions, the'specimens were further heated at a temperature below their order-disorder lattice transformation point, e.g., at about 600C, for at least 1 minute but not longer than 100 hours, and then cooled.

The permeability of the ring specimens thus heat treated was measured by a conventional ballistic galvanometer. The highest values of the initial permeability (n and the maximum permeability (p of the specimens proved to be 64,000 and 409,600, respectively. It was also found that the specimens had a considerably high hardness and a large electric resistivity.

FIG. 1A shows contours of the highest values of the initial permeability n, of the nickel-iron-niobium alloys of different compositions which were obtained by the aforesaid various heat treatments. Similar contours for the highest values of the maximum permeability p. of the nickel-iron-niobium alloys of different compositions are shown in FIG. 18 after applying the aforesaid variety of heat treatments.

FIGS. 2A, 2B, and 2C are schematic sections of FIGS. 1A and 1B, taken along the lines a-2', b-b and c-c', respectively, illustrating the highest values of the initial permeability a, and the maximum permeability along such sections.

Table I shows the physical properties of selected alloy specimens. (The details of the process for making the alloy specimens of Table 1 will be described hereinafter).

ture. Thus, there are an optimal heating temperature and an optimal heating time for each alloy composi- TAB LE 1 Saturated Residual IIystereflux Cooling magnetic sis loss density speed after d flitix Coercive (er-g per (G) Heat treatment heating Maxiensi y oiei em. per Composition at 600 C. Initial mum (G) (08.) cycle) At Elelcotsrilsc iclrpgs Tom er- Durafor ermeapermea c at ure tion minutes p bility bility At maximum flux density of field of tivity ness No. Ni Fe N1) 0.) (hour) C./hour) (us) (um) 5,000 (r 000 00. (nil-cm.) (11v) 2 1,100 3 8,100 12, 700 116,000 0,010 42.0 105 6 2 1,150 3 2, 800 10, 250 58, 800 4,110 0. 0250 J. 10 8, 7-10 45. 3 170 15. 6 4. 2 1, 250 3 400 10, 430 121, 700 4, 200 (I. 0213 13, 0 5. 0 1, 250 ll 2, 800 .30, 500 108, 200 l4. 5 5. 0 1,350 3 400 21, 150 24!], 100 3, 630 0. 0080 13. 1 6. 5 1, 250 18 100 15, 080 345, 000 I3. 5 0. 5 1, 150 3 240 34, 800 1211, 000 3, 300 0. 0160 13. 5 ti. 5 1, 250 El 800 MI, 300 302, 1100 3,500 0. 0008 13. 5 0. 5 1, 350 3 100 .20, 000 .131, 600 3, .230 0. 0082 12. 0 7. 5 1, 350 3 400 40, 300 151,000 2, 600 0. 0003 13. l 7. 5 1, 250 3 240 40, 000 86, 300 3, 360 0. 0105 13.1 7. 5 1, 250 0 800 13, 500 I01, 500 l3. 1 7.5 l, 250 18 800 34, 800 254, 300 0. 0088 11. 4 8. 0 1, 250 18 100 33, 000 354, 500 11. 4 8. 0 1, 250 18 8, 100 21, 000 200, 700 .5 11.1 8. 4 1,150 3 240 44, 500 143, 000 11. 1 8. 4 1, 250 U 240 04, 000 400, 000 .5 11. 1 8. 4 1, 250 0 3 240 42, 000 306, 400 .5 11. 1 8. 4 1, 250 I) 1 8,100 33, 500 37, 700 .5 11.1 8.4 1,350 3 400 55,100 221,800 .5 11. 1 8. 4 1,350 3 1 -100 -16. 300 207. 000 .5 12. 1 8. 4 1, 150 3 240 43, 500 .212, 000 1 10. 6 0. 3 1, 250 18 2-10 43, 520 -1, 000 1 10. 6 0. 3 1, 250 18 I 2, 800 32, 500 187, 300 .7 11.0 0.3 1,250 {I 100 53.650 231,500 7 11. 0 1). 3 1, 250 0 240 3-1, 800 301, 500 .7 10. 1 10. 2 1, 250 J 100 25,140 08, 000

1 And heated 1112400" C. for 1 hour. 3 And heated at 400 C. for 30 It is apparent from FIGS. 1A to 2C that the addition of 3.1 to 14.0 Wt.% of niobium into binary nickel-iron alloys greatly improves the magnetic properties of the alloys, and the heating of such ternary alloys at a temperature higher than 1,100C further improves the permeability of the ternary alloys. Thus, with the alloys of the present invention, extremely high initial permeability and maximum permeability can easily be obtained. For instance, alloy Specimen No. consisting of 80.5 Wt.% of nickel, 11.1 Wt.% ofiron, and 8.4 Wt.% of niobium showed an initial permeability of 64,000 and a maximum permeability of 409,600, when it was heated at l,250C for 9 hours and cooled in a furance to 600C for keeping it at 600C for 10 minutes and then cooled to room temperature at a cooling speed of 240C/hour. Such values of permeability are considerably larger than those obtainable by using conventional alloys; namely, a conventional nickel-iron alloy consisting of 78.5 Wt.% of nickel and 21.5 Wt.% of iron shows an initial permeability of 8,000 and a maximum permeability of 100,000, when it is heated at l,0501.050C and slowly cooled to 600C followed by quick cooling from 600C. Y

FIG. 3A shows the effects of different high heating temperatures and the heating time at such temperatures on the initial permeability of the ternary alloy, for the case of Specimen No. 55 of Table 1. FIG. 3B shows similar effects on the maximum permeability of the same Specimen. The values of the permeability in FIGS. 3A and 38 were determined after cooling Specimen no. 55 from the illustrated high temperature in the range of 1,050 to 1,350C in a special manner; namely, it was cooled to 600C in a furnace for keeping it at 600C for 10 minutes and then cooled to room temperature at a speed of 240C/hour. It is apparent from FIGS. 3A and 38 that the permeability is materially influenced by the high heating temperature and the duration in which the alloy is heated at such high temperaminutes.

tion, in order to maximize the permeability. More particularly, a heat treatment at a temperature below 1,100C results in comparatively low permeabilities; namely, an initial permeability not greater than 12,000 and a maximum permeability not greater than 1 10,000. On the other hand, a high temperature heat treatment at 1,100C or higher results in comparatively high permeabilities; namely, an initial permeability greater than 12,000 and a maximum permeability greater than 1 10,000.

In the figures, non-primed symbols in FIGS. 4A and 48 h 2, 2 1, 2 a u 2 3 1, and 2 p sent the permeability of the corresponding alloys, which were treated by heating at l,250C for 9 hours, cooling to 600C in a furnace, and then further cooled from 600C to room temperature at different speeds as specified by such non-primed symbols in the figures. The curves A to E were drawn by connecting such nonprimed points for the corresponding alloys.

Primed points in FIGS. 4A and 4B (A,', A B B C C C D,, D D E,', and E represent the permeability of the corresponding alloy Specimens after further treating them from the corresponding non-primed conditions, respectively. The heat treatments for the primed points were as follows.-

A, After A Specimen No. was reheated at 350C for 1 hour and cooled in air. A After A Specimen No. 10 was reheated 350C for 1 hour and cooled in air. B After 3,, Specimen No. 25 was reheated 400C for 30 minutes and cooled in air. B, After B Specimen No. 25 was reheated 400C for 30 minutes and cooled in air. C After C Specimen No. 35 was reheated 350C for 1 hour and cooled in air. C, After C Specimen No. 35 was reheated 350C for 30 minutes and cooled in air. C, After C Specimen No. 35 was reheated 400C for 1 hour and cooled in air. d, After D Specimen No. 55 was reheated 400C for 1 hour and cooled in air. D After D Specimen No. 55 was reheated 400C for 30 minutes and cooled in air.

D After D Specimen No. 55 was reheated 400C for 1 hour and cooled in air.

E, 2 After E Specimen No. 70 was reheated 400C for 2 hours and cooled air.

E After E Specimen No. 70 was reheated at 400C for 2 hours and cooled in air.

The following trends are noticed in FIGS. 4A and 48. For alloys with 3.7 Wt.% of niobium, quick cooling is necessary in order to obtain a high permeability, initial or maximum, and reheating, e.g., at 350C for 1 hour, tends to reduce the permeability. As the niobium content increases, e.g., toward 5.6 to 14.0 Wt.%, high permeabilities can more frequently be obtained by slower cooling. In general, if the alloys are comparatively quickly cooled from 600C the succeeding reheating tends to noticeably increase their permeability, while if the alloys are comparatively slowly cooled from 600C the succeeding reheating tends to jeopardize their permeability. The aforesaid trends are noticed both in the initial permeability and the maximum permeability.

FIG. 5 illustrates the hysteresis curve for the Specimen having the highest permeability, i.e., Specimen No. 55. It is apparent from the figure that the hysteresis loss of Specimen No. 55 is extremely small.

The present invention will not be described in further detail by referring to specific Examples. (Detailed explanation will be made in the following Examples on Specimens selected from those listed in Table 1, and similar treatment may be applied on non-selected Specimens for obtaining similar effects.)

EXAMPLE 1 Alloy Specimen No. 35 consisting of 80.0 Wt.% of nickel, 13.5 Wt.% of iron, and 6.5 Wt.% of niobium, as listed in Table 1, was made by using 99.8%-pure electrolytic nickel, 99.97%-pure electrolytic iron, and 99.8%-pure niobium. An ingot of the Specimen was ten metal so as to produce a homogeneous melt of the I alloy, and pouring the melt into a metallic mold having a cylindrical hole of 25 mm diameter and mm height. The ingot was hot forged at about 1,000C into 7 mm thick sheets. The sheets were hot rolled at about 600 to 900C to a thickness of 1 mm, and then cold rolled at room temperature to make them into thin sheets of 0.3 mm thickness. Rings with an inner diameter of 27 mm and an outer diameter of 35 mm were punched out from the thin sheets.

The rings thus formed were subjected to different heat treatments, as shown in Table 3. Physical-properties of the rings after the treatments are also shown in Table 3.

EXAMPLE 2 Alloy Specimen No. 55, consisting of 80.5 Wt.% of nickel, 11.1 Wt.% of iron, and 8.4 Wt.% of niobium, was made by using the same materials in a similar manner as Example 1, so as to make similar rings. Different heat treatments were applied to the rings of Specimen No. 55, as shown in Table 4, together with the physical properties of the rings thus treated.

EXAMPLE 3 Alloy Specimen No. 70, consisting of 79.7 Wt.% of nickel, 10.1 Wt.% of iron, and 10.2 Wt.% of niobium, was made by using the same material in a similar manner as Example 1, so as to make similar rings. Different heat treatments were applied to the rings of Specimen No. 70, as shown in Table 5, together with the physical properties of the rings thus treated.

In examples 1 to 3, 99.8%-pure metallic niobium was used as the starting material, but instead of such metallic niobium, ferro niobium available in market can also be used as the starting material of the alloys according to the present invention. Since the use of ferro niobium tends to make the alloy increasingly brittle, it is preferable to add a suitable deoxidizer and/or a desulfurizer into the melt of the alloy of the invention, so as to improve the ductility by deoxidation and desulfurization.

Thus, with the method according to the present invention, the heat treatment'may be completed only by a primary treatment, which consists of heating a ternary alloy with a composition falling in the specific range of the invention, in a non-oxidizing atmosphere TABLE 3 Saturated flux Residual Hysteresis density magnetic loss (erg (G) flux Coercive per cm." Initial Maximum density force -r At rnag- Electric Vickers pcrmeapermea- (G) (00.) cycle) netit rcsishard- Item bility y field of tivity ness No. Heat treatment (#m) At maximumflux density of 5,000 (i 000 0c. (all-cm.) (11v) 1 c IIcated at 1,150 C. in hydrogen for 3 hours, 34,300 120,000 3,300 0.0160 13.60 7.600 60.2 103 cooled in furnace to 600 C., and cooled to room tcmprcature at 240 C./hour. ll After I, reheated at 350 C. in vacuo for 1 hour.. 20,500 113,000 1 1 111 Heated at 1,250 C. in hydrogen for 3 hours, 15,000 106,000 7, 620 61,0 101 cooled in furnace to 600 C.. and cooled to room temperature at C./sec. IV After III, reheated at 350 C. in vacuo for 1 hour.. 20, 000 173,000 3, 380 0124 '15. T, 580 60.5 Heated at 1,250 C. in hydrogen for 0110urs, 40,300 302,800 3,500 0.0008 14.46 100 cooled in furnace to 600 C., and cooled to room temperature at 800 C./hour. \l After reheated at 350 C., in vacuo for 30 min- 32. 500 216,400 105 utcs. \'ll llcatcd at 1,250 C. in hydrogen for 1) hours, 10,400 .340, 000 3,410 0.0145 18. 66 7,000 60.0 10-1 cooled in furnace to 600 (3., and cooled to room temperature at 100 C./hour. \'lll AftcrVll, rehcatcd at 350 C. in vacuo forl hour. 11, 200 178,000 c 105 IN llcatcd at l,350 (1., in hydrogen for 3 hours 20,000 231,000 3,230 0008:! 13.10 7,550 00.3 mt

cooled in furnace, to 600 (3., and cooled to room tcnuwraturc at 400 L/hour. X Al'tcr IX, reheated at 350 (1. in vacuo for 1 hour. 18,500 138,300

TABLE 4 1 Heated at 1,150 C. in hydrogen for 3 hours, 44,500 143,000 .2, 850 0.0114 16. 05 6,530 69.0 210 cooled in furnace to 600 C., and cooled to room temperature at 240 C./hour. II After I, reheated at 400 C. in vacuofor 30 38, 000 176,000

minutes. 111 Heated at 1,250 C. in hydrogenfor 0 hours, ooled 5, 500 124, 000 6, 470 60. 5 208 in furnace to 600 0., and cooled to room temperature at 8,100 C./hour. After 111, reheated ta 400 C in vacuo for 1 hour 33,500 237, 700 '2, 640 0. 0054 0. 63 Heated at 1,250 C. in hydrogen for 0 hours, 64,000 400, 600 550 0.0038 5.00 6,550 60.3 210 cooled in furnace to 600 0., and cooled to room temperature at 240 C./h0ur. VI After \i, reheated at 400 C. in vacuo for 30 42,000 306, 400 6,520 60.0

. mrnu es. VII Heated at 1,250 C. in hydrogen for 0 hours, 39,200 346,500 '2, 730 0.0047 7.53 6,530 69.2 312 cooled in furnace to 600 0., and cooled to room temperature at G./hour. I V111, After VII, reheated at 400 C. in vacuo for 1 hour. 24, 000 .287, 400 21'! IX Heated at 1,350 C. in hydrogen for 3 hours, 55,100 221,800 2,080 0. 0036 7.47 6,530 60.4 208 cooled in furnace to 600 0., and cooled to room temperature at 400 CJhour'. X After 1X, reheated at 400 C. in vacuo-for 1 hour. 46, 300 207, 000 ..,4-10 0. 0046 8.25

TABLE 5 Saturated flux Residual Hysteresis density magnetic loss (erg (G) flux Coercive per cm. Initial Maximum density force per At mag- Electric Vickors permeapermea- (G) (oe cycle) netic rcsishard Item hility bllity (fold of tivity ncss 0. Heat treatment 0) m) At maximum flux density of 5,000 (1 000 0c. (11941111.) (11v) Heated at 1,150 C. in hydrogen for 3 hours, 11,600 55, 250 1.550 0.0142 15.62 5,250 75.5 220 cooled in furnace to 600C., and cooled to room temperature at 100 C./hour. I I After I, reheated at 400 C. in vacuo for 1 hour. 10, 300 111 Heated at 1,250 C. in hydrogen for 3 hours, 20,300

cooled in furnace to 600 C., and cooled to room temperature at 100 C./hour. 1V After 111, reheated at 400 C. in vacuo for 2 hours. 17,000 V Heated at 1,250 C. in hydrogen for 9 hours, 2,000

cooled in furnace to 600 C., and cooled to room temperature at 400 C./hour. After V, reheated at 400 C. in vacuo for 2 hours 10,250 Heated at 1,250 C. in hydrogen for 9 hours, 25,140

cooled in furnace to 600 C., and cooled to room temperature at 100 CJhour. V11I After VII, reheated at 400 C. in vacuo for .2 17,500

lOLllS. 1X Heated at 1,350 C. in hydrogen for 3 hours, 22,400

cooled in furnace to 600 C and cooled to room temperature at 100 O./hour. X After IX, reheated at 400 0.111 vacuo for 2 hours. 18, 600

treated by the aforesaid primary heat treatment, which secondary heat treatment comprises steps of heating the alloy in a non-oxidizing atmosphere or in vacuo at a temperature below the order-disorder lattice transformation point of the alloy, preferably at about 600C, for at least 1 minute but not longer than about 100 hours, and then gradually cooling,

The optimal cooling speed to obtain excellent magtent of 8.4 Wt.% which gives the highest permeability among all the Specimens, the optimal cooling speed is so slow that it is preferable to cool it in a furnace. It is one of the important features of the present invention that the outstandingly high permeability of the alloy can be produced by a very simple heat treatment.

Conventional materials for magnetic recording and reproducing heads have a shortcoming in that the passage of magnetic tape in contact with such heads tends to abrade the heads, which head abrasion may cause deterioration of the quality of the signals, e.g., sound quality, recorded or reproduced by the head. Accordingly, the alloy for magnetic heads should preferably have a high hardness and a high abrasion resistivity. Conventional nickel-iron alloys for magnetic heads have a Vickers hardness in the order of about 130, which is not high enough for ensuring a high abrasion resistivity. On the other hand, the Vickers hardness of the alloy according to the present invention increases with the niobium content, as shown in FIG. 6 and Table l, and a Vickers hardness as high as 157 to 241 can be obtained by adding 3.1 to 14.0 Wt.% of niobium. The alloy having the highest permeability, which contains 8.4 Wt.% of niobium, shows a Vickers hardness of 210. Thus, the abrasion resistivity of magnetic material for recording and reproducing heads is noticeably improved by the present invention. It is one of the important features of the present invention that the abrasion resistivity of magnetic recording and reproducing heads is improved by increasing the hardness of the alloy constituting the heads.

The electric resistivity of magnetic recording and reproducing heads should preferably be high, for suppressing the eddy current loss therein. The electric resistivity of conventional binary alloy consisting of about 79 Wt.% of nickel and about 21 Wt.% of iron is in the order of 16 pO-cm. On the other hand, with the alloys according to the present invention,'the electric resistivity comparatively rapidly increases with the niobium content, as can be seen from FIG. 6 and Table l. The use of 3.1 to 14.0 Wt.% of niobium in the alloy of the present invention results in an electric resistivity of 38 to 84 ,tQ-cm. For the niobium content of 8.4 Wt.%, which provides the highest permeability, the alloy according to the present invention shows an electric resistivity of 70 pO-cm. The high electric resistivity of the alloy is also one of the important features of the present invention.

Magnetic heads are usually made by laminating thin sheets of the alloy material, which sheets are in turn formed by rolling and cutting into suitable shape by punching. Thus, the alloy for magnetic heads should have a high workability. The alloys according to the present invention are as easily workable as conventional nickel-iron binary alloys; namely, the alloy of the invention can easily be forged, rolled, drawn, swaged, or punched.

The high hardness of the alloy according to the present invention makes the alloy particularly suitable for magnetic recording and reproducing heads, as pointed out in the foregoing. Furthermore, the outstandingly high permeability and the high electric resistivity of the alloy of the invention are also attractive in conventional electric and magnetic devices of various other types.

The contents of nickel, iron, and niobium are restricted to 70.0.to 84.8 Wt.%, 5.0 to 25.5 Wt.%, and 3.1 to 14.0 Wt.%, respectively, according to the present invention, because the alloy composition in the aforesaid range produces a high permeability and a high hardness suitable for magnetic heads, but alloy compositions outside the aforesaid range result in too low values of permeability and hardness to use the alloy for magnetic beads.

The suitable contents of the ingredients in the alloy according to the present invention will now be described in further detail.

1. 70.0 to 84.8 Wt.% of nickel:

With the nickel content of 70.0 to 84.8 Wt.%, excellent magnetic properties can be achieved, i.e., an initial permeability s, of 64,000 and a maximum permeability s, of 409,600. With nickel content less than 70.0 Wt.%, the initial permeability s, and the maximum permeability a, are reduced to levels below 3,000 and 5,000, respectively. On the other hand, with nickel content in excess of 84.8 Wt.%, a comparatively high maximum permeability p, can be obtained but the initial permeability t, becomes less than 3,000. Thus, the nickel content is restricted to 70.0 to 84.8 Wt.%.

2. 5.0 to 25.5 Wt.% of iron:

With the iron content of 5.0 to 25.5 Wt.%, excellent magnetic properties can be obtained. On the other hand, with iron content of less than 5 .0 Wt.% or in excess of 25.5 Wt.%, the initial permeability a, and the maximum permeability t, are always below 3,000 and 5,000, respectively. Thus, the iron content is restricted to 5.0 to 25.5 Wt.%.

3. 3.1 to 14.0 Wt.% of niobium:

With the niobium content in the aforesaid range, excellent magnetic properties and hardness can be obtained. On the other hand, with the niobium content of less than 3.1 Wt.%, it becomes difi'icult to ensure the Vickers hardness l-lv to be not smaller than 150. When the niobium content increases in excess of 14.0 Wt.%, the initial permeability p, and the maximum permeability t, become smaller than 3,000 and 5,000, respectively. The excessively high niobium content also results in the deterioration of the workability of the alloy, especially its forgeability and rollability. Thus, the niobium content is restricted to 3.1 to 14.0 Wt.%.

In short, the alloy according to the present invention consists of 70.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% iron, 3.1 to 14.0 Wt.% of niobium (instead of metallic niobium, ferro niobium in market may also be used), and an inevitable amount of impurities. An ingot of the alloy of the invention may be made by pouring a melt of the alloy into a suitable mold. The ingot may be shaped into a desired form by working it at room temperature or at an elevated temperature, for instance by forging, rolling, drawing, swaging, or the like.

After the shaping, the alloy is heat treated by heating it at 800C or higher (preferably higher than l,l00C) in a non-oxidizing atmosphere, e.g., hydrogen, or in vacuo for at least 1 minute but not longer than about hours, and cooled to room temperature at a cooling speed of from lC/hour to 100C/second, preferably l0C/hour to l0C/second, depending on the alloy composition. For certain alloy compositions, the alloy may be reheated to a temperature below its orderdisorder lattice transformation point, e.g., below about 600C, for at least 1 minute but not longer than about 100 hours. With such heat treatment, high permeability including an initial permeability a, of 64,000 and a maximum permeability of 409,600 can be obtained. In addition to the high permeability, the alloy according to the present invention has a number of properties suitable for magnetic recording and reproducing heads; namely, a comparatively high electric resistivity, a high hardness, and a high workability at room temperature and at an elevated'temperature in terms of forgeability, rollability, drawability, and swageability.

With the alloy of the present invention, extremely high values of initial and maxiumu permeability can be generated by using the following composition and applying any of the following heat treatments to the alloy.

al. An alloy consisting of 70.0 to 84.8 Wt.% of nickel, 5.0 to 25.5 Wt.% of iron, 3.1 to 14.0 Wt.% of niobium, and an inevitable amount impurities is heated at a temperature above 800C, preferably above l,lC, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, cooled in a furnace to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600C, and cooled to room temperature from the intermediary tempterature at a cooling rate in a range of lC/hour to 100C/second, preferably C/hour to 10C/second. Whereby, one can obtain an initial permeability of about 3,000 to 64,000 and a maximum permeability of about 5,000 to 409,600.

a2. After the cooling to room temperature, the alloy of the preceding item (a1) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, so as to generate the permeabilities of the item (a1).

bl. An alloy consisting of 75.3 to 82.2 Wt.% of nickel, 9.2 to 20.6 Wt.% of iron, 3.1 to 10.8 Wt.% of niobium, and an inevitable amount impurities is heated at a temperature above 800C, preferably above l,l00C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, cooled in a furnace to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600C, and cooled to room temperature from the intermediary temperature at a cooling rate in a range of 1C/hour to 100C/second, preferably 10C/hour to 10C/second. Whereby, one can obtain an initial permeability of about 10,000 to 64,000 and a maximum permeability of about 50,000 to 409,600.

b2. After the cooling to room temperature, the alloy of the preceding item (bl) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, so as to generate the permeabilities of the item (bl 01. An alloy consisting of 78.3 to 81.8 Wt.% of nickel, 09.6 to 15.2 Wt.% of iron, 4.8 to 10.4 Wt.% of niobium, and an inevitable amount impurities is heated at a temperature above 800C, preferably above l,l00C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, cooled in a furnace to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600C, and

cooled to room temperature from the intermediary temperature at a cooling rate in a range of lC/hour to C/second, preferably 10C/hour to 10C/second. Whereby, one can obtain an initial permeability of about 20,000 to 64,000 and a maximum permeability of about 100,000 to 409,600.

c2. After the cooling to room temperature, the alloy of the preceding item (01) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, so as to generate the permeabilities of the item (cl).

d1. An alloy consisting of 79.0 to 81.4 Wt.% of nickel, 10.1 to 14.2 Wt.% of iron, 5.7 to 9.8 Wt.% of niobium, and an inevitable amount impurities is heated at a temperature above 800C, preferably above l,l00C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, cooled in a furnace to an intermediary temperature slightly above the order-disorder lattice transformation point of the alloy, for instance to about 600C, and cooled to room temperature from the intermediary temperature at a cooling rate in a range of lC/hour to 100C/second, preferably 10C/hour to 10C/second. Whereby, one can obtain an initial permeability of about 30,000 to 64,000 and a maximum permeability of about 200,000 to 409,600.

d2. After the cooling to room temperature, the alloy of the preceding item (d1) may be reheated at a temperature below its order-disorder lattice transformation point, e.g., below about 600C, in a non-oxidizing atmosphere or in vacuo for at least 1 minute but not longer than about 100 hours, so as to generate the permeabilities of the item (d1).

What is claimed is:

1. An alloy for magnetic recording and reproducing heads, consisting essentially of 70.0 to 84.8 Wt. of nickel, 5.0 to 25.5 Wt. of iron, and 3.1 to 14.0 Wt. of niobium, said alloy having a Vickers hardness of greater than and having an initial permeability above 3,000 and a maximum permeability above 5,000, and a degree of order greater than 0.1 but less than 0.6.

2. An alloy according to claim 1, wherein the nickel content is 75.3 to 82.2 Wt.%, the iron content is 9.2 to 20.6 Wt.%, and the niobium content is 3.1 to 10.8 Wt.%.

3. An alloy according to claim 1, wherein the nickel content is 78.3 to 81.8 Wt.%, the iron content is 9.6 to 15.2 Wt.%, and the niobium content is 4.8 to 10.4

4. An alloy according to claim 1, wherein the nickel content is 79.0 to 81.4 Wt.%, the iron'content is 10.1 to 14.2 Wt.%, and the niobium content is 5.7 to 9.8 Wt.%.

5. An alloy according to claim 1, wherein the initial permeability is greater than 12,000 and the maximum permeability is greater than 1 10,000.

6. An alloy according to claim 1, wherein the electric resistivity is greater than 38 (l-cm. 

2. An alloy according to claim 1, wherein the nickel content is 75.3 to 82.2 Wt.%, the iron content is 9.2 to 20.6 Wt.%, and the niobium content is 3.1 to 10.8 Wt.%.
 3. An alloy according to claim 1, wherein the nickel content is 78.3 to 81.8 Wt.%, the iron content is 9.6 to 15.2 Wt.%, and the niobium content is 4.8 to 10.4 Wt.%.
 4. An alloy according to claim 1, wherein the nickel content is 79.0 to 81.4 Wt.%, the iron content is 10.1 to 14.2 Wt.%, and the niobium content is 5.7 to 9.8 Wt.%.
 5. An alloy according to claim 1, wherein the initial permeability is greater than 12,000 and the maximum permeability is greater than 110,000.
 6. An alloy according to claim 1, wherein the electric resistivity is greater than 38 Mu Omega -cm. 